Waste water from restaurants, bakeries, food processing industries etc. contain much fat. The fat, which at first is of low viscosity and often emulsified, becomes separated and solidifies, when the waste water gets cold. The solidified fat often causes stoppage in the sewers. Most municipalities with municipal sewage nets, receiving waste water from restaurants and food processing industries, with high fat content in the waste water, are therefore limiting the fat concentration in the waste water and demand installation of fat separators to maintain the limit.
Beside fat the waste water contains several other substances in dissolved or suspended form as surfactants and alkali from cleaning agents, starch, proteins and fibres from food rests etc. In the fat separator the fat is separated as a solid comparatively hard cake contaminated with other substances. When the fat separator's space for fat is full, it has to be emptied. Before emptying, the fat cake has to be broken up. More often than not it happens that this breaking up does not became good enough to allow all fat to be eliminated. Remaining fat pieces follow the waste water and gather in the parts of the sewer where the current is weak, and form with other contaminants stoppages, causing at least as large problems as the fat stoppages mentioned.
The separated fat contains large amounts of both unsaponified and saponified fat. Such a mixture is very unfavourable from the reworking point of view especially as the reworking is disturbed by the contaminants mentioned. Usually the separated fat has to be disposed of.
Many trials have been done to decompose the fat, to be more easily handled, by using enzymes and several other chemicals. The decomposition products, which are soluble or form stabile dispersions in water, do not cause problems in the sewer and give no problems in the sewage works. Exceptions from this rule are fatty acids, which are said to cause growth of so called filiform bacteria, which may cause sludge swelling and sludge escape. The success with enzymes has been limited. Chemicals of other kinds are often causing problems in the conduits and in the sewage works.
Trials with living bacteria cultures have been more successful. Especially have cultures with a broad spectrum of starch degrading, protein degrading and fat degrading bacteria shown good results. European patent application No. 0 546 881, French patent application No. 2 659 645 and French patent application No. 2 708 923 treat some different aspects of this technique. Of those publications EP 0 546 881 and FR 2 708 923 relates to the treatment of fat in the diluted form that is found in waste water, while FR 2 695 645 relates to fat that has been separated from waste water by flotation.
According to all these publications the ultimate objective is complete decomposition of fat to water, carbon dioxide and biomass. In any cases one neglects the fact that the fatty acid part of the fat is an industrially useful raw material, with a substantial market value, if it can be recovered in an acceptably pure form.
Microorganisms with the capacity to split proteins, starch and fat are not found among bacteria, only, but also among fungi, for instance. Often fungus cultures can be superior to bacteria cultures. For instance, fungus cultures are characterised by higher tolerance for toxins and have higher reaction rates. In a preferred embodiment of this invention the microbe culture consists at least in part of fungus culture.
The growth conditions for microorganisms in a fat separator are not optimal. The capacity to reproduce under given circumstances differs between different microbe species. Thus, occasional additions do not suffice to maintain a well-balanced composition in the microbe culture. Repeated additions are necessary. Earlier these additions have been made at the inlet of the fat separator.